Lewis acids are among the most powerful initiators for hydrocarbon conversion reactions. Such catalysts have been used in liquid, gaseous and solid form, and have been supported or immobilized on various polymeric and inorganic substrates, including, for example, silica gel, alumina, graphite and various clays.
Both supported and unsupported Lewis acid catalysts have been used with varying degrees of success for initiating alkylation reactions, in the carbocationic polymerization of olefins, such as isobutene and in hydrocarbon isomerization and cracking reactions. Supported Lewis acid-type components, such as titanium trichloride, titanium tetrachloride, vanadium tetrachloride, and hafnium tetrachloride also have been used in Ziegler-type polymerization reactions where stereoregular or crystalline polymers are the desired polymeric product. In such Ziegler-type processes, the catalyst components are often supported on an inorganic oxide which has been pretreated, for example, with an alkyl halide silane, to reduce the number of free hydroxy groups on the surface of the support. Ziegler-type processes which are carried out in the presence of such pretreated supports are disclosed, for example, in U.S. Pat. Nos. 5,143,883; 4,374,753; and 4,565,795.
However, in spite of the general advances made in the fields of alkylation, polymerization, isomerization and cracking catalysis, there is a continuing need for highly efficient catalyst systems having a selectively controllable activity, as well an ability to be recycled or reused in such processes. The present invention was developed pursuant to this need.